Periodic Trends in the Properties of the Elements 9.9

Tro's "Introductory Chemistry", Chapter 9 Trends in Atomic Size Either volume or radius. Treat atom as a hard marble. As you traverse down a column on the periodic table, the size of the atom increases. Valence shell farther from nucleus. As you traverse left to right across a period, the size of the atom decreases. Adding electrons to same valence shell. Valence shell held closer. Tro's "Introductory Chemistry", Chapter 9

Trends in Atomic Size, Continued

Be (4p+ and 4e-) Mg (12p+ and 12e-) Ca (20p+ and 20e-) Group IIA 2e-

Tro's "Introductory Chemistry", Chapter 9 Period 2 2e- 1e- 3 p+ 2e- 4 p+ 2e- 3e- 5 p+ Li (3p+ and 3e-) Be (4p+ and 4e-) B (5p+ and 5e-) 6 p+ 2e- 4e- 8 p+ 2e- 6e- 10 p+ 2e- 8e- C (6p+ and 6e-) O (8p+ and 8e-) Ne (10p+ and 10e-) Tro's "Introductory Chemistry", Chapter 9

Example 9.6 – Choose the Larger Atom in Each Pair C or O Li or K C or Al Se or I? Tro's "Introductory Chemistry", Chapter 9

Practice—Choose the Larger Atom in Each Pair. 1. N or F 2. C or Ge 3. N or Al 4. Al or Ge Tro's "Introductory Chemistry", Chapter 9

Practice—Choose the Larger Atom in Each Pair, Continued. N or F, N is further left N or F C or Ge N or Al, Al is further down & left N or F C or Ge N or Al Al or Ge? opposing trends N or F C or Ge, Ge is further down Tro's "Introductory Chemistry", Chapter 9

Tro's "Introductory Chemistry", Chapter 9 Ionization Energy Minimum energy needed to remove an electron from an atom. Valence electron easiest to remove. M(g) + 1st IE  M1+(g) + 1 e- M+1(g) + 2nd IE  M2+(g) + 1 e- First ionization energy = energy to remove electron from neutral atom; 2nd IE = energy to remove from +1 ion; etc. Tro's "Introductory Chemistry", Chapter 9

Tro's "Introductory Chemistry", Chapter 9

Trends in Ionization Energy As atomic radius increases, the ionization energy (IE) generally decreases. Because the electron is closer to the nucleus. 1st IE < 2nd IE < 3rd IE … As you traverse down a column, the IE gets smaller. Valence electron farther from nucleus. As you traverse left to right across a period, the IE gets larger. Effective nuclear charge increases. Tro's "Introductory Chemistry", Chapter 9

Trends in Ionization Energy, Continued Tro's "Introductory Chemistry", Chapter 9

Example—Choose the Atom in Each Pair with the Higher First Ionization Energy Al or S, Al is further left 1. Al or S 2. As or Sb 3. N or Si 4. O or Cl, opposing trends Al or S As or Sb N or Si, Si is further down and left Al or S As or Sb, Sb is further down

Tro's "Introductory Chemistry", Chapter 9 Practice—Choose the Atom with the Highest Ionization Energy in Each Pair 1. Mg or P 2. Cl or Br 3. Se or Sb 4. P or Se Tro's "Introductory Chemistry", Chapter 9

Tro's "Introductory Chemistry", Chapter 9 Practice—Choose the Atom with the Highest Ionization Energy in Each Pair, Continued 1. Mg or P 2. Cl or Br 3. Se or Sb 4. P or Se ? Tro's "Introductory Chemistry", Chapter 9

Electron Affinity Energy change for the process of adding an electron to a neutral atom to form a negative ion Higher negative values = more E released Becomes more negative from L to R Becomes less negative from top to bottom

Electronegativity Ability of an atom to attract toward itself the electrons in a chemical bond Elements with high electronegativity have a greater tendency to attract electrons than do elements with low

Electronegativity Trends Increase from L to R Increase from bottom to top